Decimate's Un-Subdivide mode no longer works #72906

New Issue

Todd Gillissie · 2020-01-04T23:45:23+01:00

Todd Gillissie commented

2020-01-04 23:45:23 +01:00

System Information
Operating system: Darwin-18.7.0-x86_64-i386-64bit 64 Bits
Graphics card: AMD Radeon Pro 580 OpenGL Engine ATI Technologies Inc. 4.1 ATI-2.11.20

Blender Version
Broken: version: 2.81 (sub 16), branch: master, commit date: 2019-12-04 11:32, hash: f1aa4d18d4
Worked: 2.80

Short description of error
Decimate's Un-Subdivide mode no longer works.
I used to use Un-Subdivide a lot in Blender 2.8, but it has stopped working in 2.81.

Exact steps for others to reproduce the error
Create a plane.
Subdivide it a few times.
Add the Decimate modifier.
Switch to Un-Subdivide mode.
Increase iterations.
Notice no effect.

**System Information** Operating system: Darwin-18.7.0-x86_64-i386-64bit 64 Bits Graphics card: AMD Radeon Pro 580 OpenGL Engine ATI Technologies Inc. 4.1 ATI-2.11.20 **Blender Version** Broken: version: 2.81 (sub 16), branch: master, commit date: 2019-12-04 11:32, hash: `f1aa4d18d4` Worked: 2.80 **Short description of error** Decimate's Un-Subdivide mode no longer works. I used to use Un-Subdivide a lot in Blender 2.8, but it has stopped working in 2.81. **Exact steps for others to reproduce the error** Create a plane. Subdivide it a few times. Add the Decimate modifier. Switch to Un-Subdivide mode. Increase iterations. Notice no effect.

Todd Gillissie commented

2020-01-04 23:45:23 +01:00

Added subscriber: @Gillissie

Stanislav Blinov commented

2020-01-05 10:09:12 +01:00

Added subscriber: @Stan_Pancakes

Stanislav Blinov commented

2020-01-05 10:09:12 +01:00

Cannot confirm on Linux, Decimate's Un-Subdivide behaves the same between 2.79, 2.80 and 2.81 here.

Pasang Bomjan commented

2020-01-05 12:58:02 +01:00

Added subscriber: @Pasang

Pasang Bomjan commented

2020-01-05 12:58:02 +01:00

I can't reproduce it here in windows either. It works fine..

Philipp Oeser commented

2020-01-06 11:23:17 +01:00

Added subscriber: @lichtwerk

Philipp Oeser commented

2020-01-06 11:23:17 +01:00

Changed status from 'Needs Triage' to: 'Needs User Info'

Philipp Oeser commented

2020-01-06 11:23:17 +01:00

Also cannot reproduce.

Just to make sure:

Could you share your .blend file with the decimate modifier?

Also cannot reproduce. Just to make sure: - Could you share your .blend file with the decimate modifier?

Todd Gillissie commented

2020-01-07 06:08:20 +01:00

Un-Subdivide Bug.blend

Uploaded blend file.

Created plane.
Pressed tab to go to edit mode on plane.
Right-click, click Subdivide.
Increased "Number of Cuts" to 10.
Pressed Command-T to convert all quads to triangles.
Pressed tab to exit edit mode.
Switched to wireframe mode to see polygons.
Added "Decimate" modifier.
Switched Decimate mode to Un-Subdivide.
Increased "Iteration" and saw no difference.

[Un-Subdivide Bug.blend](https://archive.blender.org/developer/F8263896/Un-Subdivide_Bug.blend) Uploaded blend file. 1. Created plane. 2. Pressed tab to go to edit mode on plane. 3. Right-click, click Subdivide. 4. Increased "Number of Cuts" to 10. 5. Pressed Command-T to convert all quads to triangles. 6. Pressed tab to exit edit mode. 7. Switched to wireframe mode to see polygons. 8. Added "Decimate" modifier. 9. Switched Decimate mode to Un-Subdivide. 10. Increased "Iteration" and saw no difference.

Todd Gillissie commented

2020-01-07 06:31:56 +01:00

Link to video of me doing the above steps: https://www.youtube.com/watch?v=5PS2HefA9ww

Stanislav Blinov commented

2020-01-07 06:39:58 +01:00

Changed status from 'Needs User Info' to: 'Archived'

Stanislav Blinov closed this issue

2020-01-07 06:39:58 +01:00

Stanislav Blinov self-assigned this 2020-01-07 06:39:58 +01:00

Stanislav Blinov commented

2020-01-07 06:39:58 +01:00

In #72906#843061, @Gillissie wrote:
...
5. Pressed Command-T to convert all quads to triangles.
...

The modifier won't work with such topology:

It is intended for meshes with a mainly grid-based topology (without giving uneven geometry). If additional editing has been done after the subdivide operation, the results may be unexpected.

This is not a bug.

> In #72906#843061, @Gillissie wrote: > ... > 5. Pressed Command-T to convert all quads to triangles. > ... The modifier [won't work ](https://docs.blender.org/manual/en/latest/modeling/modifiers/generate/decimate.html#un-subdivide) with such topology: > It is intended for meshes with a mainly grid-based topology (without giving uneven geometry). If additional editing has been done after the subdivide operation, the results may be unexpected. This is not a bug.

Todd Gillissie commented

2020-01-07 06:44:36 +01:00

All I know is that it worked before I upgraded to 2.81.

Stanislav Blinov commented

2020-01-07 06:49:05 +01:00

Neither 2.79b, nor 2.80 un-subdivide such a triangulated plane. As the documentation says, you may get some results from a non-grid, non-quad geometry, but you can't rely on that.

Neither 2.79b, nor 2.80 un-subdivide such a triangulated plane. As the documentation says, you **may** get some results from a non-grid, non-quad geometry, but you can't rely on that.

Todd Gillissie commented

2020-01-07 06:52:36 +01:00

I guess it's possible that I was working with Un-Subdivide-friendly meshes before, but it seems very odd that I would have so much success with it then suddenly no success.

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Decimate's Un-Subdivide mode no longer works #72906